I have just bought an item from a website in the USA)
The payment was done using SSL.

However I have just realised that I hadn't ran my firewall at startup
(like I almost always do !)
I think I had been online for about 30-45 mins until I realised that I hadn't turned on my firewall.
And by that point I'd already made my purchase.

So I'm a little worried. (I am very cautious when it comes to security).
(I understand that Ubuntu usually doesn't run many/any services
unless I set up them myself. Unlike Windows. And I haven't set anything
up myself - to my knowledge)

Well, at least you're running Linux. That in itself is a sensible safety measure... Most malware and other attacks are specifically tailored to Win-OS vulnerabilities, so can't work on Linux anyway.

You can turn on the firewall at boot by default, google 'round for a HOWTO

Mind, I don't have a firewall on my PC's, but I do have one on my router. Most manufacturers offer this as standard and usually these are pretty secure, especially if you purchase a semi-professional version (or "home and small business" as they'd like to call it) by specialised manufacturers like Netgear, Linksys/Cisco, etc.

I've never felt the need of a firewall in any of the PCs I use, because I always use a router with an effective firewall built in. You can easily check whether you have any open ports by running Shields Up.

GeordieJedi wrote:However I have just realised that I hadn't ran my firewall at startup(like I almost always do !)I think I had been online for about 30-45 mins until I realised that I hadn't turned on my firewall.And by that point I'd already made my purchase.

I think you may be mixing up an application that configures your firewall with the firewall itself.

What do you mean when you say you had not run the firewall at startup?